Geovane Silva holds his son Gustavo Henrique, who has microcephaly, at the Oswaldo Cruz hospital in Recife, Brazil, the focus of a major Zika outbreak.Photograph: Ueslei Marcelino/Reuters

Pregnant women infected with Zika are 20 times more likely to give birth to children with central nervous system birth defects such as abnormally small heads, a study from the US Centers for Disease Control and Prevention has found.

Researchers compared data about early brain malformations, microcephaly, eye defects, and other central nervous system problems in babies born in 2013 – before Zika reached the US – to the children of mothers infected with Zika in 2016.

For healthy mothers, central nervous system birth defects appeared in about three of every 1,000 live births. By contrast, central nervous system abnormalities appeared in 60 infants and fetuses per 1,000 pregnancies when mothers were infected with Zika.

Mosquito season is approaching in North America, just as cuts have been proposed to scientific research. The findings also come following a controversial decision by the US army to license a taxpayer-funded Zika vaccine to pharmaceutical giant Sanofi Pasteur.

Dr Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, Texas, said the CDC’s findings were “very consistent” with those of an earlier study from scientists in Brazil.

“That was a clear indication that Zika is a really bad actor,” said Hotez. “This is causing a level of severe congenital birth defects associated with bad neurologic outcomes, even more than we previously believed.”

Global health officials first raised alarms about Zika’s possible link with severe birth defects, including microcephaly, in late 2015 in Brazil. Since then, the virus has spread to North America, the Caribbean, Mexico and Central America. The US territory of Puerto Rico has been especially hard-hit.

Areas along the coast of the Gulf of Mexico are also considered vulnerable, with long mosquito seasons and known populations of Aedes aegypti mosquitoes, the species known to transmit Zika. Mosquito season is nearly year-round in some areas of the US, especially southern Florida.

Florida and Texas have both struggled to contain the virus in their states. As of 2016, Miami-Dade County had 259 locally acquired cases of Zika, according to the Miami Herald. Cases where local mosquitoes transmitted the disease were also discovered in Palm Beach, Pinellas and Broward counties.

In Texas, 310 cases of travel and locally acquired Zika were found between 2015 and 2016, including 187 pregnant women, according to the Texas Department of Health and Human Services. The virus was also transmitted locally by mosquitoes in Cameron and Brexar counties.

Experts have warned that infection rates could be much higher than publicly acknowledged. When Zika was first found in the US, testing for the virus was difficult and time-consuming, and no region was undertaking pre-emptive surveillance.

“We know there are at least 300-plus documented cases in south Florida and south Texas, but again because we did not do active surveillance for Zika virus infection on the Gulf coast Texas or Florida where Aedes aegypti mosquitoes are, we still don’t know what the consequences of the 2016 epidemic were,” said Hotez.

“We’ll have to wait and see if babies are born with severe neurologic defects starting around May or June, because it’s a delayed epidemic. There’s a lag.”

In the CDC study published on Thursday, researchers used data from 747 infants born in Georgia, Massachusetts and North Carolina in 2013-2014 to find the frequency of central nervous system disorders in mothers who are not infected with Zika. For every 1,000 live births, three were born with defects like those associated with Zika, researchers found.

However, when studying 442 children born to women probably infected with Zika, 26 infants had such birth defects, a 20-fold increase in frequency and roughly 6% of the pregnancies studied.

Authors of the study said that 47 children with neurological abnormalities have already been to likely Zika-infected mothers in the United States.

The news comes as researchers at the CDC are hurriedly studying the disease, with science research now broadly threatened by the Trump presidency. In a 2018 budget request, the White house requested a 10.5% cut in discretionary funding to agencies such as the National Institutes of Health, through which significant Zika research funding is funneled.

Meanwhile, a group of lawmakers are questioning the US army’s decision to exclusively license a Zika vaccine researched using taxpayer funding to Sanofi Pasteur, over concerns that the pharmaceutical giant could price the vaccine too high for the most vulnerable people to afford.